Benadryl can take anywhere from 15-60 minutes to kick in for adults, depending on all sorts of factors like your metabolism, age, body weight etc. If you are a 5 foot tall, 100 lb girl you might be around the 15 minute side. If you are a 64 250 lb guy, obviously it would take longer. You should monitor yourself and find out how long it takes for you personally, so you know for the future.

Long-Term Effects of Tylenol PM; How Tylenol Works. Print this Diphenhydramine is sold under the brand name Benadryl and Like most systems in the body, the muscular system does not work in isolation. How to Take Tylenol & Aleve Detail:http://www.ehow.com/how-does_4926089_tylenol-pm-work.html